The present invention pertains to an improved flue box assembly for use in conjunction with heating plants to safely insure substantially complete combustion of the fuels in the heating plant, and more particularly, to such a device employing a movable damper means having flue openings in the damper plate.
It has become increasingly important for energy conservation to provide a device which will insure substantially complete combustion of all the fuel vapors in heating plants, or, hereinafter, furnace boxes, such as home furnaces, water heaters, boilers, etc. In U.S. Pat. No. 4,136,676, a flue box device for use in conjunction with the exhaust outlet of a heating plant is described which is particularly suited for safely accomplishing this purpose. That device has been found to exhibit vast improvements in creating safe back pressures to retain the waste gases and fuel vapors within the combustion chamber of the heating plant until virtually all of the fuel is consumed into usable heat. When installed in the pathway of the exhaust or waste gas conduit emanating from the heating plant or heat source, that device provides a movable damper plate which retains the bulk of the gases within the combustion chamber to the point of insuring maximum energy efficiency. The movable damper can safely assume an open position to provide an enlarged chamber during an excessive back pressure or explosive situation. A flue opening is provided in that damper plate which is diametrically smaller than either the inlet or outlet apertures to the housing. In an explosive situation, the increased upward draft pressure of unburned and possible waste gases will cause the damper plate to swing open thereby safely avoiding excess vapor build up and the possibility of an explosion or suffocation.
Prior to the commercially successful flue box as disclosed in U.S. Pat. No. 4,136,676, various types of devices had been developed which were designed to accomplish fuel efficiency.
For example, U.S. Pat. No. 1,196,117, illustrates a damper plate which is employed in the exhaust line of a furnace and consists of a pivotally mounted plate seated over a sheet metal exhaust tube. The damper plate retains the bulk of the exhaust or waste gases within the furnace assembly until they are combusted. It will be noted in connection with this disclosure, that the external perimeter of the sheet metal waste pipe is provided with a plurality of circumferentially disposed recesses in order to permit the escape of some of the flue gases during combustion, while the damper plates insures that the bulk of the gases will remain in the furnace until fully combusted. Similar devices are shown by U.S. Pat. No. 1,580,106 wherein a damper plate is apertured to permit the exhaust of some waste gases during the combustion process.
During any back pressure or explosive situation, means must be provided for waste gases to immediately exhaust themselves from the furnace so that a destructive explosion will not occur. It is for this reason that damper plates which are provided along the exhaust pathway of the tubing are provided in a pivotable or otherwise movable fashion. It is intended that during a back pressure or explosive situation, the pivotally mounted damper plate will move to a fully open position and permit the waste gases to be immediately exhausted from the combustion chamber. The difficulty with the prior art devices is that the diametric size of the exhaust pipe immediately above the damper plate has been virtually the same as or less than the diametric sizing of the exhaust pipe immediately below the damper plate. As a result, there is still a danger that the exhaust gases, during a back pressure or explosive situation cannot be quickly exhausted through the waste pipe, and hence, the danger of an explosive situation with regard to the entire furnace is still present.
The commercially successful flue box as disclosed in U.S. Pat. No. 4,136,676, provides a safe solution to this energy conservation problem. The damper plate of that device will be automatically fully opened in the event of a fuel vapor build up problem or a delayed ignition of the fuel vapors to safely eliminate the dangers of explosion and suffocation.
During start up of a relatively cold heating plant, in the sense of not having any substantial amount of retained heat, the draft or venting capabilities for drawing off waste gas products is at its lowest point. During a cold start-up of a heating plant, the combustion chamber and flue conduit surfaces are cold causing stratification of the denser unburned fuel products near the surfaces of the flue box and exhaust conduit. As the pilot begins to burn the fuel, and produce hot exhaust gases, a channeling effect occurs wherein a central column of hotter gases is created which may cause a build up of unburned fuel vapors below the damper plate in the flue box assembly disclosed in U.S. Pat. No. 4,136,676. This phenomena is more apparent in devices containing a fluidic heat transfer system, such as boilers or water heaters, which cool much more quickly thereby decreasing the natural draft effect which would be facilitated by a warm heating plant.